Patients 18 years of age or older who are admitted to Suburban Hospital in Bethesda, Maryland, for angioplasty of one or more of the blood vessels in the neck or skull may participate in this study. Participants must be able to undergo a brain MRI. Within 24 hours before their angioplasty, patients will provide a medical history and have a physical examination and brain MRI. The physical examination and MRI will be repeated within 24 hours after the angioplasty.